Precipitation of solid phase calcium carbonates and their effect on application of seawater <i>S<sub>A</sub></i>–<i>T</i>–<i>P</i> models
At the present time, little is known about how broad salinity and temperature ranges are for seawater thermodynamic models that are functions of absolute salinity (<i>S<sub>A</sub></i>), temperature (<i>T</i>) and pressure (<i>P</i>). Such models rely...
| Main Authors: | , , |
|---|---|
| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2009-07-01
|
| Series: | Ocean Science |
| Online Access: | http://www.ocean-sci.net/5/285/2009/os-5-285-2009.pdf |
| _version_ | 1828833200915349504 |
|---|---|
| author | R. Feistel F. J. Millero G. M. Marion |
| author_facet | R. Feistel F. J. Millero G. M. Marion |
| author_sort | R. Feistel |
| collection | DOAJ |
| description | At the present time, little is known about how broad salinity and temperature ranges are for seawater thermodynamic models that are functions of absolute salinity (<i>S<sub>A</sub></i>), temperature (<i>T</i>) and pressure (<i>P</i>). Such models rely on fixed compositional ratios of the major components (e.g., Na/Cl, Mg/Cl, Ca/Cl, SO<sub>4</sub>/Cl, etc.). As seawater evaporates or freezes, solid phases [e.g., CaCO<sub>3</sub>(s) or CaSO<sub>4</sub>2H<sub>2</sub>O(s)] will eventually precipitate. This will change the compositional ratios, and these salinity models will no longer be applicable. A future complicating factor is the lowering of seawater pH as the atmospheric partial pressures of CO<sub>2</sub> increase. A geochemical model (FREZCHEM) was used to quantify the <i>S<sub>A</sub></i>−<i>T</i> boundaries at <i>P</i>=0.1 MPa and the range of these boundaries for future atmospheric CO<sub>2</sub> increases. An omega supersaturation model for CaCO<sub>3</sub> minerals based on pseudo-homogeneous nucleation was extended from 25–40°C to 3°C. CaCO<sub>3</sub> minerals were the boundary defining minerals (first to precipitate) between 3°C (at <i>S<sub>A</sub></i>=104 g kg<sup>−</sup>) and 40°C (at <i>S<sub>A</sub></i>=66 g kg<sup>−</sup>). At 2.82°C, calcite(CaCO<sub>3</sub>) transitioned to ikaite(CaCO<sub>3</sub>6H<sub>2</sub>O) as the dominant boundary defining mineral for colder temperatures, which culminated in a low temperature boundary of −4.93°C. Increasing atmospheric CO<sub>2</sub> from 385 μatm (390 MPa) (in Year 2008) to 550 μatm (557 MPa) (in Year 2100) would increase the <i>S<sub>A</sub></i> and t boundaries as much as 11 g kg<sup>−1</sup> and 0.66°C, respectively. The model-calculated calcite-ikaite transition temperature of 2.82°C is in excellent agreement with ikaite formation in natural environments that occurs at temperatures of 3°C or lower. Furthermore, these results provide a quantitative theoretical explanation (FREZCHEM model calculation) for why ikaite is the solid phase CaCO<sub>3</sub> mineral that precipitates during seawater freezing. |
| first_indexed | 2024-12-12T17:12:38Z |
| format | Article |
| id | doaj.art-7cd69bbf6de643908fb95435710afcf5 |
| institution | Directory Open Access Journal |
| issn | 1812-0784 1812-0792 |
| language | English |
| last_indexed | 2024-12-12T17:12:38Z |
| publishDate | 2009-07-01 |
| publisher | Copernicus Publications |
| record_format | Article |
| series | Ocean Science |
| spelling | doaj.art-7cd69bbf6de643908fb95435710afcf52022-12-22T00:17:51ZengCopernicus PublicationsOcean Science1812-07841812-07922009-07-0153285291Precipitation of solid phase calcium carbonates and their effect on application of seawater <i>S<sub>A</sub></i>–<i>T</i>–<i>P</i> modelsR. FeistelF. J. MilleroG. M. MarionAt the present time, little is known about how broad salinity and temperature ranges are for seawater thermodynamic models that are functions of absolute salinity (<i>S<sub>A</sub></i>), temperature (<i>T</i>) and pressure (<i>P</i>). Such models rely on fixed compositional ratios of the major components (e.g., Na/Cl, Mg/Cl, Ca/Cl, SO<sub>4</sub>/Cl, etc.). As seawater evaporates or freezes, solid phases [e.g., CaCO<sub>3</sub>(s) or CaSO<sub>4</sub>2H<sub>2</sub>O(s)] will eventually precipitate. This will change the compositional ratios, and these salinity models will no longer be applicable. A future complicating factor is the lowering of seawater pH as the atmospheric partial pressures of CO<sub>2</sub> increase. A geochemical model (FREZCHEM) was used to quantify the <i>S<sub>A</sub></i>−<i>T</i> boundaries at <i>P</i>=0.1 MPa and the range of these boundaries for future atmospheric CO<sub>2</sub> increases. An omega supersaturation model for CaCO<sub>3</sub> minerals based on pseudo-homogeneous nucleation was extended from 25–40°C to 3°C. CaCO<sub>3</sub> minerals were the boundary defining minerals (first to precipitate) between 3°C (at <i>S<sub>A</sub></i>=104 g kg<sup>−</sup>) and 40°C (at <i>S<sub>A</sub></i>=66 g kg<sup>−</sup>). At 2.82°C, calcite(CaCO<sub>3</sub>) transitioned to ikaite(CaCO<sub>3</sub>6H<sub>2</sub>O) as the dominant boundary defining mineral for colder temperatures, which culminated in a low temperature boundary of −4.93°C. Increasing atmospheric CO<sub>2</sub> from 385 μatm (390 MPa) (in Year 2008) to 550 μatm (557 MPa) (in Year 2100) would increase the <i>S<sub>A</sub></i> and t boundaries as much as 11 g kg<sup>−1</sup> and 0.66°C, respectively. The model-calculated calcite-ikaite transition temperature of 2.82°C is in excellent agreement with ikaite formation in natural environments that occurs at temperatures of 3°C or lower. Furthermore, these results provide a quantitative theoretical explanation (FREZCHEM model calculation) for why ikaite is the solid phase CaCO<sub>3</sub> mineral that precipitates during seawater freezing.http://www.ocean-sci.net/5/285/2009/os-5-285-2009.pdf |
| spellingShingle | R. Feistel F. J. Millero G. M. Marion Precipitation of solid phase calcium carbonates and their effect on application of seawater <i>S<sub>A</sub></i>–<i>T</i>–<i>P</i> models Ocean Science |
| title | Precipitation of solid phase calcium carbonates and their effect on application of seawater <i>S<sub>A</sub></i>–<i>T</i>–<i>P</i> models |
| title_full | Precipitation of solid phase calcium carbonates and their effect on application of seawater <i>S<sub>A</sub></i>–<i>T</i>–<i>P</i> models |
| title_fullStr | Precipitation of solid phase calcium carbonates and their effect on application of seawater <i>S<sub>A</sub></i>–<i>T</i>–<i>P</i> models |
| title_full_unstemmed | Precipitation of solid phase calcium carbonates and their effect on application of seawater <i>S<sub>A</sub></i>–<i>T</i>–<i>P</i> models |
| title_short | Precipitation of solid phase calcium carbonates and their effect on application of seawater <i>S<sub>A</sub></i>–<i>T</i>–<i>P</i> models |
| title_sort | precipitation of solid phase calcium carbonates and their effect on application of seawater i s sub a sub i ndash i t i ndash i p i models |
| url | http://www.ocean-sci.net/5/285/2009/os-5-285-2009.pdf |
| work_keys_str_mv | AT rfeistel precipitationofsolidphasecalciumcarbonatesandtheireffectonapplicationofseawaterissubasubindashitindashipimodels AT fjmillero precipitationofsolidphasecalciumcarbonatesandtheireffectonapplicationofseawaterissubasubindashitindashipimodels AT gmmarion precipitationofsolidphasecalciumcarbonatesandtheireffectonapplicationofseawaterissubasubindashitindashipimodels |